Automatic telephone system



Se .at. 27 1 J, wlcKs AUTOMATIC TELEPHONE SYSTEM Original Filed Abril 28. 1921 5 Sheets-Sheet 1 Sept, 27,1927

- J. wlcKs AUTOMATIC TELEPHONE SYSTEM 5 7 m a QR Lu m i Sept. 27,1927. ,797

. J. WICKS AUTOMATI C TELEPHONE SYSTEM S'Sheets-Sheet 3 Original Filed April 8 1 Inu5n ELF- Jul-Ln Hicks 74 W B Sept. 27, 192?,

J. WiCK AUTOMATiC TBLEPHOM: SYSTEM T e Ai 5 Sneaks-Sheer. 4

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Original Filed Aural 28. 1921 QQ www ILL 1 QQ W) h b25401 mmvmqmk Patented Sept. 27, 1927.

UNITED STATES PATENT OFFICE.

JOHN WICKS, OF OAK PAR-K, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, .TO AUTO- MATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed April 28, 1921, Serial No. 465,101. Renewed January 25, 1926.

The present invention relates in general to automatic telephone systems, but more especially to such automatic systems as include private automatic exchanges; and the 1 5 object of the invention, broadly stated, is the provision of novel arrangements in a system of the above character whereby a toll operator in a main exchange or toll ofiice can interconnect toll lines terminating at her position with subscribers lines which terminate in. the private automatic exchanges.

In my prior application,- Serial No. 389,- 683, filed June 17, 1920, which became Patent No. 1,604,372 dated Oct. 26, 1926, I have shown and described a system of the same general type, in which a private branch exchange trunking system is provided comprising, in the case of any particular private automatic exchange, a group of trunk lines which is accessible to the toll operator through the out-going toll service trunks, and which is also accessible to the main exchange subscribers through the regular exchange trunking system. The trunk lines in this group, since they must provide for two radically different classes of service, are somewhat complicated and expensive to install and maintain. The present invention may be considered to be an improvement on the system shown in the application referred to and was conceived with the object in mind of providing a simpler and cheaper construction, which under certain circumstances would be better adapted .to commercial use. In carrying out this object the regular local traflic and the long distance or toll traflic to the private automatic exchange are kept separate to a vgreat'extent instead of being handled overa single group of combination trunk lines. A relatively large group of trunks is provided for the regular localcalls between the main and branch exchange subscribers, and a separate and much smaller 7 group of trunks is provided for handling the toll connections to the private branch subscribers. Thus the trunk line in. each group since they are used for only one class of calls are comparatively simple.

The invention goes further than this, how- 00 ever, and, by a special arrangement in which the regular trunk lines are made available for use in emergencies in handling toll traffic, although on a slightly less efiicient basis from a transmission standpoint, the number "..of toll trunks require in a given, f s i duced much below the number that would otherwise be necessary. According to this feature of the invention the toll second selectors (such as transmission selector E, Fig. 3) have access to a small group of toll trunks onthe particular level assigned to the pri- 'vate automatic exchange to which these trunks extend, the toll trunksbeingterminated in the first few contact sets of such level so as to give them the preference; and these toll selectors also have access to a certain number of the regular main to branch exchange trunk lines, which are terminated 1D the remaining sets of contacts in the level in question, and which are taken for use in toll connections therefore only when the regular toll trunks are busy. The exact number of trunk lines to each group in any given case Wlll of course depend onthe amount of traffic, but where the size of the private automatic exchange does not exceed 100 lines it is intended to provide only'a single toll trunk line under normal conditions, and the system .described herein is so illustrated.

The foregoing sets forth in a general way the object and scope of the invention; There are a number of minor features necessarily involved which are not now specifically mentioned, but which'together with the broad features outlined above Will be fully explained hereinafter withreference to the ac companying drawings.

For a proper understanding of the drawings, Figs. 15, inclusive, should be arranged in'order with the corresponding lines at the ends thereof in alignment, and when so disposedthere is shown a complete circuit connection from a calling toll operators position shown in Figs. 4 and 5 is located in the private automatic exchange. I

Referring now to Fig. 1, the toll operatorsfcord circuit 0 is a cord circuit of standard. ty e which is used for connecting tel]. lines with the toll operators outgoing- Tl", Fig. '5; The equipment at the attend access to thetoil -trunl: X, but also ha's acexplained in the course of the explanationof the operation of the system; Notoll' line" is shown since it is considered unnecessary in View of the well known and simple character of such circuits, but one of the outgoing toll service trunks is shown extending from the jack J to the toll first selector D; This selector switch is of the ordinary 'Strowger vertical and rotary type. and is operated according to thewell-known two Wire system of controL'a's is shown and described in the patent to Jacob'sen No. 1,349,381, granted Aug. 10, 1920. In iew or the fact that a elector of this type is o1d'andw 11 k own the switch has been indicated by a dotted rectangle and the circuits" are not shown. w e i v v The toll first selectors have acce's's to a number foit" groups of trunk lines, the trunk 'li'ii'esof each grou extending to toll second electors (the so called transmission selectors). by. way of associated relay groups. One of these trunk lines is shown extending from the contac't set comprising bank con- ,tacts 26 28, inclusive, by way of the relay group BG, Fig. 2, 'tothe transmission selector E, Fig. The relay group RG is individiial to the transmission selector E and would ordinarily be incorporated inthe same switch structujre wit'h the selector were it not for the fact that the large number of relays makes it advisable to mount certain oi these on a 'sep'aratebase. The transinis'sion selector E is a vertical and rotary selector switch 01' the type described in the patent previously mentioned;

As will be understood from the general explanation already given, the trans-mission selector E has access, at a ce'rtainldesignated level, to a toll trunk 'line extending to the qpriigate automatic exchange under considera'tfion. This toll t'r'unk line 15 1nd 'cated by the reference character X, and extends :tr'oin the bank contacts 18 4 andl137 in the bank ofthe toll transmission selector E by Way of certain key and relay equipment in the attendents cabinet at the private automatic exchange, Fig. 4, to the incomin connector ants cabinet, as it is coininonly cal-led, has been designed especially for use in con'nfection with a toll trunl of this type and the operation of all the apparatus will be desoribedin detail. The incoming 'connect'or BY is a Strowger Vertical and rotary switch of. the usual mechanical construct on. A The ,circuit's care shown in full and will be described. I p

The transmission selector E not only has cess to the regular main to branch exchange "trunk lines which are used for setting up ordinary connections. One of the trunk linesin this group is indicatedby'thelreferonce character Z and extends from the bank contact set comprising bank contacts 150- 152, inclusive, located in" the bank of a second selector of the regular mainexcha e trunking system, by way of the repeat-er Fig. 3, and the" key and relay equipment at the attendants cabinet in the branch ex change, Fig. 4, to the incoming connector H l ig. 5. Therepeater F serves to provide "a holding circuit for anyse'cond selector which connects with the associated trunk lineand is used'primarily to avoidtlre'ne'ce'ssi'ty of having three conductors in the trunk line extending to the branch exchange. The ap aratus at the a'ttendants cabin'ehF-ig. 21-, which is associatedwith the trunk line Z of a generalitype'which has been'already used to a considerable exte na'the essential features ojt" which are shown and described in the UPS. patent to Powell; No. 1,356,010

granted Oct. 19, 1920.- The incoming conmain to branch exchange trunk lines are terminated, such as the incoming connector H, have common access to all the. lines in the private automatic exchange. "One or these lines is the line extending to substation A which is an ordinary automatic s'ubstation of the usualtyp'e, having the calling device S for the purpose, or control-ling the ai'itomatio switches.

The s'wi'tchC 's individual to the line of substation Aand is a rotary Switch of t'lie well known type in which the wipers have no normal position and move in 'a "forward direction only; The function of the switch G is to extend the associate'd' line when calling to a trunk line leading-to an idle selector connector, which is useclfor com- 7 pleting local' 'co1inections and also for connecting with the trunk lines extending to the' in'a'in exchange. In view 0 the "fact that selector connectors of the type mentioned are wellknown none oft'hese switches are shown herein, but reference i made to thepatent to Ray st 1211., No. 1,4: 8,6178, issued Sept. 18, 1923, which shows-a selector connect-or .sui'etable for use in the present situation. i i

The 'trirnk lines to which the selector connectors in the branch exchange have access are the same trunk lines 'hereinbeiere mentioned as being'provic'led for hand liln g regular main "to branch exchange traific, one of whidhisthe trunk li'ne Z, and it will be unde r'sto'o'd then that these trunk lines are two 'waytrunkline's. The set of bank contacts comprising contacts 200-202, inclusive, in

the upper left hand corner of Fig. 5, are located in the bank of one of the local selector connectors. When the trunk line is taken for use by a selector connector in the branch exchange connection isextended thereto by way of these bank contacts or a multiple thereof, and the line switch C, Fig.3, at the main exchange end of the trunk line is operated to extend the connection to an idle first selector in the main exchange. The line switch C it maybe stated is similar in construction to the line switch C.

' It is thought that the apparatus, havlng been described more or less in general, Wlll be better understood when described in connection with a detailed description of its operation. For this purpose itwill be assumed that the toll operator receives a ticket calling for a connection between the subscriber at substation A and some other subscriber, who may be in a distant city. Any approved method of calling thedistant subscriber may be used and accordingly It will not be explained in the present description, and we shall concern ourselves only with the establishing of the connection to the substation A. To make such a call, the toll operator inserts the'plug of an idle cord'cireuit, the plug P of cord circuit O for example, into the jack of an outgoing toll service trunk, the jack J for example. Assuming that she does as above noted, the line and release relays (not shown) of the selector D immediately energize and the latter prepares the switch for operation in the usual manner. The circuit of the line relay of the said selector includes conductor 21, the upper right winding of the repeating coil associated with the cord circuit, polarized relay 10, the lower right winding of the said repeating coil, and conductor 22. The flow of current in this case through the polarized relay 10 is not in such a direction as to operate the said relay. The operator now throws her key K and thereby includes the calling device S in the circuit, instead of the polar relay 10 and the associated windings of the repeating coil.

The operator may now manipulate her calling device S in accordance with the first digit of the desired number, whereupon the selector D operates in the usual manner to raise its wipers to the desired level and rotate them to pick out an idle trunk line. e shall assume that the trunk line terminating in the bank contacts 26 to 28, inclusive, is the first one found idle, and consequently the one selected. That being the case, the connection is extended by Way of trunk conductors 29 and 31, upper and lower left windings of repeating coil T, conductors 78 and 79, normally closed contacts controlled by armatures 57 and 59, armature 61 and its resting contact and normally closed contacts controlled by armature 62, conductors 73 and 76, and the resting contact of armature 117 and said armature to the upper and lower windings of line relay 100 of the transmission selector E. The line and release relays 100 and 101' of the said selector imme diately energize and the latter, at armature 109, places ground on release trunk-conductor 30 so as to hold the selector E in its operated position. As a further result of the energization of release relay 101 it prepares the switch for operation at armature 111 and places ground on conductor 74 at armature 110, thereby closing a circuit for the lower winding of electro polarized relay 33. This winding alone, however, consisting of a small number of turns of high resistance, is not able to operate the said relay.

The operator may now operate her calling device, in accordance with the second digit of the desired number, thereby interrupting the circuit of the line relay 100 of selector E a corresponding number of times. Each time line relay 100 deenergizes it closes, at armature 107, the following circuit for the vertical magnet 125: from ground by way of armature 107 and its resting contact, armature 111 and its working contact, armature 122 and its resting contact, slow acting series relay 102, and vertical magnet 125 to battery. By the operation of'the vertical magnet, thev switch shaft and wipers are raised step by step until the latter stand opposite the desired, level of bank contacts. Relay 102 energizes in series with the vertical magnet and being slow acting retains its armature attracted throughout the vertical movement. Upon'energizing, relay 102 closes the following circuit: from'grounded conductor 74 by Way of the Working contact of armature 112, contact 127, and the lower winding of the ring out off relay 37 to battery. Upon energizing, relay 37 locks itself to conductor 74 at armature65 and opens at armature 64 and 66 the connect-ion to the upper winding of the said relay and to the intermittent generator lead. Returning now to relay 102, as a further result of its operation, it closes, upon the closureof the vertical off normal springs, a circuit for the stepping relay 103. Stepping relay 103, upon energizing, closes at armature 116, a locking circuit for itself including armature 119 and its resting contact ..and the resting contact of the armature of rotary magnet 126 and the said armature; and, at armature 115, prepares the circuit of the rotary magnet 126. At the end of the vertical movement, slow acting relay 102 deenergizes and closes a circuit for the rotary magnet 126. Rotary magnet 126, upon energizing, steps the wipers 130 to 133, inclusive, into engagement with the first set of bank contacts in the level opposite which they areraised. The rotary magnet also breaks the circuit of the stepping relay 103 which deenergizes and breaks thecircuit of the rotary magnet,

' test wiper 132 is in engagement is busy or idle, If the test contact is busy it has a ground potential on it, and the stepping relay 103 energizes again and the same cycle of. operation is repeated over and over until an. idle or undergrounded test contact is reached. V'hen an idle set of contacts is reached, the switching relay 105 energizes in series with the stepping relay 103 over the following circuit: from ground by way of grounded conductor 74, switching relay 105, resting contact of the armature of rotary magnet. 126 and said armature, on normal. contacts 114, and stepping relay 103 to battery. Relay 103, however, due to its relatively small number of turns and comparatively stiff adjustment, does not energize over this circuit. In the present case, however,,we shall assume that the first set of contacts, which are the contacts 134 to 137, inclusive, are idle when the. selector is operated as above described. That being the case, the energization of switching relay 105 extends the connection to the trunk line X at armatures 120 and 124iand places ground on the test wiper 132 at armature 123, so as to make the trunk line X busy to the other selectors having access to it, this groundpotential extending by way of conductor 14.3 to multiple test contacts in the banks of the other selectors. As a further result of the energization of switching re- Ilay 105, it closes at armature 121 the following circuit: from ground bv way of bank contact 135, Wiper 131, Working contact of armature 121 and said armature, conductor 72, and relay 32 to battery. Relay 32, upon energizing, opens the normally closed bridge connection hack to the operator.

around the condenser associated with the right-hand windings of repeating coil T, at armature 50, and at 'armatu-res and 51 places the upper and lower windings of battery feed relay 35 in bridge of the said condenser. As a further result of the energisation of relay 32, it closes at armature 52 a circuit for reversing relay 3%. Relay 34, upon energizing, locks itself to the grounded conductor 74; at armature and at armatures 57 and 59 reverses the conductors 78 and 7 9. as regards their connection with the windings of line relay 100 of selector E; at the sametime introducing the, resistances 67 and 68 into the circuit ofthe said relay. This latter operation is performed merely to decrease the amount of current flowing through the established In response to the before mentioned reversal of the connections of conductors 78 and 79, assuming that the operator has returned the weave-7 key K to normal position, the polarized l'eir io incord circuit opi at s ts m tures thereby lighting the supervisory lampL, which apprises theoperator of the fact that the call has so far been successful.

When the operator, is ready to signal the attendant in the private branch exchange,

she operates her ringing key on the right hand end of cord circuit 0, thereby prousual ringing circuit and ringing current is intermittently sent out over the trunk line X. The small capacity condenser 80 which is bridged from armature 6.6 to its working contact allows enough ringing current to pass through to inform the calling operator that the attendantv operator at th'e private branch exchange is being signalled.

The ringing current thus sent out over the trunk line causes the relay 300 of the connector H, which is in bridge of the con- I ductors of the trunk line X, to energize. Upon energizing, relay 300 closes a looking circuit for itself by way of armature 317 and its resting contact, resting-contact of armature 316 and the said armature, and armature 311 and its Workin'g contact; and, at armature 312,. closes the circuit of the answering lamp L in front of the attendant operator. The attendantoperaton'upon noting the lighted condition of lamp. L, throws the listening key K thereby operating the springs224s, 225 and 227. 3 Spring 225, upon operating, closes a bridge across conductors 259 and 265 as follows: from conduct-or 2.65 by way of spring 225 and its working contact, conductor 264'andrelay 301 to conductor 259.

In the relay group BE: in the-main: exchange, the closure of this directflcurrent bridge across the conductors of trunk line Z results in the operation of the ring cut-off relay v3-7. Upon energizing, relayj37 closes .a locking circuit for itself at armature 65,

and at armatures 64 and 66 removes the, intermittent ringing current from the said trunk lineand extends, .at the said armatures,the connection to the ripper andJlower windings of the battery feed relay 35,. Re-

lay 35 immediately energizes, over thefitrunk line X and the before .menti'oned'bridge across the said trunk line at the branch exchange, and, upon so doing, closes a local energizing circuit for line relay 100. of selector E at armature 62 and its, wni'l ing circuit;

upon so doing, closes, at armature 313 and its Working contact, a circuit for itself in dependent of the spring 225 of key K and at armature 316 opens the locking circuit of ringing response relay 300, allowing the said relay to deenergize and extinguish the answering lamp L..

The two operators may now converse with each other and the attendant operator,iupon learning who the desired subscriber is, finds out the correct number and throws the calling key K It will be noted vthat, with keys K and K both operated, the windings of battery feed impedance 233 are bridged across the conductors of trunk line X. This is done so as to feed talking battery'to the called subscriber in case the attendant operator makes a call byway of the connector H when there is no transmission selector up, on the distant end of the trunk line X.

This causes no harm to result in the present case, however, for impedance 233 is so connected that it feeds battery out in parallel with relay 35 of relay group RG5, As a further result of the operation-of key IK? it closes at spring 229 the circuit of callingdevice switching relay 220. Upon energiz ing, relay 220 switches the circuit of the calling device S from a loop to a grounded As a still further result of 'theoperation of key K it closes at spring232 and its workingcontact a circuit for the holding lamp L and the said lamp accordingly becomes lighted; A branch of the circuit of lamp'L extends by way of conductor 282' to battery through release relay 302 of the connector H. Release relay 302, upon energizing, closes, at armature 315 and'its working contact, a multiple point in the circuit of relay 301, closes at armature 317 and its working contact a circuit for the supervisory lamp L byway of armature 3'23 and its resting contact, and conductor 261; opens a point in the circuit of release: magnet 338, at ar1nature318,"and at the said'armature and its working contact prepares an energizing circuitfor the switchin rela 310 and aflockin circuit for the C7 y a busy relay 308; and at armature 319 and its working contact completes the following circuit for the impulsing relay 303: from ground by Way of armature 221 of relay 220, calling device S, conductor 210, spring 231 and" its Working contact, conductor 263, armature 319 and its working contact, and impulsing relay 303 to battery. Impulsing relay 303, upon energizing, opens, at armature 320, a point in the circuit of vertical magnet 324 before thesaid'magnet has time to energize and closes at the said armature a multiple point in the circuit of release relay 302.

The attendant operator may now operate her calling device S in accordance with the first local digit of the desirednumber, there'- by producing a number of interruptions in the circuitv of impulsing relay 303. In response to the interruptions thus produced, the impulsing relay 303 deenergizes a like number of times, and at each deenergization closes, atarmature 320 and its resting contact, the following circuit for the vertical magnet 324: from ground by way of arma-' ture 317 and its working contact, armature 320 and its resting contact, vertical off nor mal springs 329 and 327, slow acting series relay 306, and vertical magnet 324 to bat' tery. By the operation of the vertical magnet, the switch shaft and wipers are raised step by step until the latter stand oppositev and serves'to maint'ain the circuit of the vertical magnet 32 1 intact after the ofi normal springs 327329, inclusive, have shifted,

as they doupon the first vertical'step. )At' the end of the vertical movement, relay 306 deenergizes and shifts'the impulsing circuit from the vertical totherotary magnet.

The attendant operator may now operate" the calling device S in accordance with the neXt and last digit of the desired number,

whereupon a corresponding number of impulsesfare delivered tothe rotary magnet 339' by way of the followingcircuit: from ground through armature 317 and its work ing contact, armature 320 and its resting contact, ofl enormal'springs 329 and 328,"

armature 325 and its resting contact,'resting contact of armature 334 and said armature,

armature 343 and its restingcontact, and

rotary magnet 339 to battery. By the opera-' tion of the rotary magnet the Wipers 3,47%

349, inclusive, are rotated step'by step until" they come to rest 'on the bank contacts 37 .7 379, inclusive, which are the ones in' which the line of substation A terminates. The slow acting relay'309is energized in multiple' with the rotary magnet 339 and opens;

the circuitof thejupper winding-ofswitch j ing relay 310' at armature 336, at the same time completing a .circuit from test Wiper 3458 to thebusy'test relay 308, a'ndat armature 337 and its Working contact, serves to maintain the circuit of the rotary magnet intact even though the'busy relay 308 energizes due to the Wiper 348 passing over grounded test contacts. 7

The operation now depends upon Whether the line of substation A is busy or idle. If it is busy there is a ground potential on test contact 37 8 and the busy test relay 308 is accordingly energized. Assuming that such is the case, sl w acting relay 3G9, upon deenergizih eieeee, er the norm ll closed contacts coiitrolled by enmtufesee, the following locking circuit for relay 308: from s mindhby'i ey.etgeWM 318 and t working contact, arniaturel333aiid iteweri ingcontact, normally closed contacts controlled by arinatur'e 336, and relay 308 to battery; This locking circuit is closed in order that relay 308 will not deenergi'ze' later and allow the connector H to cut in on the line of substation A after it has become idle. As .a further result of the energization of relay 308 it connects, at armature 335 and its Working contact a lead from abusy signal ling machine to'the lower'heavy talking conducton Since such machines are well known, it has, for the sake of simplicity, beeh omitted from the drawings. It Will ufliee to say that by this operation an audible'b' l'sy Signal is sent 'backto the attendant operator to inforrn her of the busy condition of the lineof substation A. Upon hearing this busy signal the operator may re lease the connector H and try to reach the desired subscriber by calling another nearby SllbStLtiOIl. I

In the present case, however, We may assurnetha'tthe line of'substation A is idle when called, Under these 'circu'rnstances, when the slew acting relay 309 'deenergize's it closes, atarmatiire 336 and its resting contact the renewing ci cuit for the up e winding of switchihg relay 310 from ground by Way of armature 318' and its Working Contact, ar'i'natur'e333 and its resting eonmet, upper winding of relay 310, resting contact of. armature @336 and said armature,

test wipersis, test-contact 378, private norniahconductor 375, switching relay 380 of the line switch C, and steppingmagnet' 382 "to, battery. Switching relays 310 and 380 energize in series with each other, and the latter 'cl'earsythe'line switch C of its normal L battery and ground connections at a'rni'atur'es 383 and 385. 'It'ihay befstated here that; due-"to dine-chemical interlocking device ("not show betweenthe immatures er relays 3'80 and 381, the 'arinatures of switching relay 380 are" able to operate only about half Way at this time and accordingly the wipers of the line switch are not connected uh Y ale-en rgizes, somewhat 'elewly'; ei'vi figto theretarding effect-0f "the copper slug on In "the connector" switching relay" of armature 317 and its Working contact;

groundsthe test Wiper 348 at armature'zea so as to make the called line busy to the other connectors; and at arinatures 340and 346 completes the connection to the line" wipers'347 and 349. The resting c ontact 10f m niature 332, as 'indicate'dby the plus-and minus si n, is assumed to be connected to an interrupted generator lead coining from a'r nging machine similartotheone shown r'e'iit is intermittently sent out to'rifig' the bridged bell at the called substation. The

operator that the called subscriber is being signalled.

ii hen the called subs riber responds by removing his receiver trr'ii'r'i'the s'W'itchhodk,

the ring cut-oil relay 307 immediately energizes and closes a locking circuit for itself at armature 331', and atarmatures330 and 332 disconnects the line wi ers from the upper Winding of the said relay and' from the ringing lead and connects 'themto the conductors 259 and 265 of trunk line X.

The su'pervisory'relay 3'05 immediately e'ner gizes and at armature 323' eXtingui'shes the supervisory lamp L at the same time closing a circuit for relay Relay 304, u'pon energi'zing, closes a-locking-circuit for itself at armature 322, and at armature'321 opens a point in the circuit of relay 301. The attendant operator and the called sub scribernow converse Witheach other, talking battery being supplied to the transmitter V at. substation A by thejlow wound batt ry feed relayseef relay roup R6 in multiple with the before 'rnentioned ir'npedance 1 The attendant-operator finds out Whether or notthe person who ,answere'dzthe telehone-is; the one wanted and, assuming he is;

she ap'prais'es the t'oll op'eratojrj of the fact and restores the keys K and K? tonormal thereby removing theirnpedance coil'233 and relay 'SOIYf-roni in bridge of the con duetors of trunk line The key'Kiuppn v returning to normal position, ejpe' s the em cult of relay" 220 at spring 2529 allowing it to deenei gize; and at th normally closed contacts controlled by spring'23l establishes the-fellowmg holdihgeircuit for the ihii r;

pulsing relay 303 of the-connector "H z'it'rom ground by' way of'the release spring 222 and its: resting Contact, a normally closed conta'cts controlled by spring 231, ccwndi'i'ctor F 263 armature 31'9 and its Working Contact,

Will be noted that the releaseirelay 302doe s not havethe'ii'sual copper slug on'it. This,

iinpdlsing;relay -e03 ee e eeaee f -g r 7-,

' from his telephone.

she may insert the plug P of the cord circuit 0 into a suitable jack and from thence extend the connection in any well known or preferred .manner. After the connection has been thus extended and the other subscriber has answered, the two subscribers converse with each other as .desired, the talking circuits that are shown being outlined by the heavy conductors.

. Ordinarily when a subscriber finishes his conversation with another subscriber he hangs up the receiver, but .in the present case, in order to explain an added function of certain parts of the circuits shown in the drawings, We shall assume that the subscriber at substation A fails to replace his receiver upon the 'switchhook at the end of the conversation. With that, condition existing if the toll operator, upon getting the usual disconnect signal from the other subscriber, should remove the plug P from the jack J the connection will not be released and the attendant operator at the private branch exchange will not be notified, unless certain provisions tending to overcome this difliculty are made. The toll operator, upon receiving a disconnect signal. from the other subscriber, and, upon failing to receive the usual disconnect signal from the subscriber at substation A, operates hers listening key K so as to ascertain whether or not the subscriber at substation A is still holding the receiver .to his ear. Assuming that she tries to talk to him but gets no response, she takes it for granted t at he has gone away In order to signal the attendant operator at the private branch eX- change, the toll operatorope'rates key K in such a direction as to project ringing current out over the established connection thereby operating ringing response relay 36 in relay group RG which, upon energizing, unlocks ring cut oil relay 37. Ring cut off relay 3?, upon deenergizing, projects ringing current out over trunk lineX. It will be noted that, since the receiver is off at this time atsubstation A, theusual energizing circuit is closed for ring out 01f relay '3? as soon as it deenergizes. This does not cause it to energize again, however, for the current flow through its upper winding is just sufficient, to operate armature and accordingly is insuificient to operate the more stiil ly adjusted armatures 64 and 56. When the toll operator restores her ringing key,

relay 36 deenergizes thereby closing the locking circuit of relay 37 which immediately pulls all the Way up and removes the interrupted ringing current from the trunk line X. While relay 37 is in a dc.- energized condition,the ringing current, in flowing out to the called substation, passes through the low Wound supervisory relay 305 in the connector H. This relay is so adjusted that its armature 323 responds .to the ringing current. Each time the arn1ature 323 falls back a circuit is closed over conductor 261 for the supervisory lamp L and the attendant operator is thereby notified that the toll operator is signalling for her. Upon noting the flickering of supervisory lamp L the attendant operator throws her listening key and finds out what the toll operator desires and upon learning that the subscriber at substation A has failed to replace his receiver she may operate her release key and release the connector H in a manner to be described here inat'ter. I I

From the above it will be deduced that, should the subscriber at substation A hang up his receiver and in case the toll operator wishes to call him back to the telephone for, some reason, when ringing current is pro jected out over the connection the bridged. bell at substation A is operated in the usual manner. It is obvious that in this case the attendant operator is signalled also. However, she need onlyv throw her listening key and ascertain whether or not the toll operator desires to speak with her, or with the subscriber at substation A- I y In the ordinary course of events, when the-conversation is completed the subscriber at substation A replaces his receiver upon the switchhook, thereby opening the circuit of battery feed relay 35, in the relay group 'BG, and supervisory relay 305 of the con nector H. Relay 35 upon deenergizing closes again the previously described cir-, cuit for line relay lOO of the selector E, the said circuit extending back by way of conductors 78 and 79 to the .toll operator, and at the same time opens the local holding circuit for the said line relay. \Vhen this is done'current begins to flow again in the toll operators cord circuit and the polarized relay 10 is accordingly reoperated to light thesupervisory lamp L. The toll operator, upon perceiving the disconnect signal, pulls down the connection. WVhen the plug is removed from jack J the circuit of line relay 100 of selector E is broken. Upon deenergizing, line relay 100'opens at armature 107 the circuit of slow acting release relay lOl. Upon deenergizing, relay 101 removes ground, at armature 109, from release trunk conductor3O thereby allowing the intervening selector D to release in the usual manner, at the same time removing ground from conductor 'Z'tat armature 110 whereupon the following relays deenergize; reversing relay 34 and ring cut oii' relay 37 ofthe relay group RG, and switching relay 105 oi selector E. Switching relay 105, upon deenergiz'ing, opens, at armature 121, the circuit of relay 32 of relay group BG and'the said' relay deenergizes. As a further result of the deenergization of release relay 101 closes at armature 111, a circuit for the release'magnet 108 in multiple with relay 1'04. Relay 104, upon energizing, opens at'armature 119 a point in the circuit of stepping relay 103 so as to prevent an accidentaloperation ot' .the said stepping relay at this time, at the same time closing a locking circuit for itself and for the release magnet 109 in series with the off normal spring 113.;As a further result of the energization of-relay 1041 it open a point in the-test circuit at armature 113, and at armature 11'7 opens a'point in the circuit of linerelay 100, toguard against its energizetionas a result of condenser discharges. By the operation of the release magnet 108 the switch-shaft and wipers are restored to normal position, the circuit of the said magnet and relay 104 being opened at oii' normal spring 113 when the shaft reaches normal position.

In the connector H, supervisory relay 305' upon deenergizing lights the supervisory lamp L and the attendant operator, upon noticing the lighted condition of the said lamp, throws her listening key so as to make sure that no one is on the line and upon discovering that no one is, she momentarily throws the said key to the opposite position, thereby separating the spring 222 from its resting contact, after which she may restore the said key to normal. Spring 222 upon operating opens the circuit of ima pulsing relay 303 of connector H and the said relay accordingly deenergizcs and, atarmature 320, opens the circuit of release relay 302 which upon deenergizing opens, at armature 319, apoint in the circuit of impulsing relay 303. As a further result of the deenergization of release relay 302 it opens at armature 317 the circuit of supervisory lamp L as well as the locking circuits of relays 307 and 310, whereupon the said'lamp becomes extinguished and the said relays deenergize. As a still further resul't-otthe deenergization oi relay302 it closes, at armature 318, the circuit of release magnet 338 by way of off normal contacts 326. By the operation of the release magnet the switch shaft and wipers are restored to normal position, the circuit of the release magnet being opened at oii normal contacts 326 by the switch shaft when it reaches normal position. The enthe connection is now released and the apparatus is ready for another call.

which the trunk line Z is one, which as before stated handled the regular .trafiic to and fromihe private branch exchange. .As,

is seen in .F ig. 3, the trunk line X term'inate's in the-first set otbank contacts in the levelin which it is wired, while the trunk line Z terminates in the second set, it being understood that other trunk lines similar :to

the trunk line Z terminatein the following sets of contacts. 'Bearing these facts in mind. we shallassume that, in the call .just described, the'trunk line X is busy duezto its being seized by some other selector, similar to the selector E, when the selector E rotates its wipers to find an idle trunk. That being the case the wipers of selector E-do not stop'onthe firstiset of contacts but rotate automatically to test the-succeeol-' ing sets. Wi e shall assume iurtherthat the trunk line Z is idle at thistime. Accordingly, the wipers of the sele'ctor E, upon reaching thebank contacts 138 to 141, inclusive, are rotated no further and the switching relay upon energizing as horeinbefore explained, extends the-connection to the said trunk line Z. When the switching relay 105 energizes; itxcloses at armature 121, a point in the circuit of relay 5320f relaygroup-HG. ln the present case, however, the wiper 131 .:engages an ungrounded contact and accordingly the-said relay is not energized.

Upon taking'up the operation of switching relay 105 in detail, we find that'th'e said relay, upon energizing, places ground on test contact-'140,"in the usual manner so as to makethe trunk line Z busy to the'switc'hes having access' to it; It will be noted that this busy potential extends byway of private normalconductor192 to the test'contact 151.

By means of the ground potential on test contact 151 and its multiples in the'banks of the selectors'having access to therep'eater F the said repeater and consequently the trunk line'Z is made busy to the said selectors."

Abranch ofthis circuit extends to battery through the switchii'ig relay 1760f therline switch C and the stepping magnetite. Switching relayf 17 6, 4 removes, at armatures 17-8 'and'lSO, the normal battery and ground connections from the trunk line Z at this point. As a still further resultof the energiz'a'tion of switch ing relay 105 the following-bridge is placed across theconductorso'f-trunk line Z, From the lower? conductor of-trunk line'Z, byway upon energizing,

of bank cont-act 14:1, wiper 133, armature 124 and its working contact, conductor 77, armature 66 and its working contact, lower right winding of repeating coil T, upper winding of electro polarized relay 33, resting contact of armature 50 and said armature, upper right winding of repeating coil T, working contact of armature 6 1 and said armature, armature 1.06 and its working contact, working contact of armature 120 and said armature, wiper 130, and bank contact 138, to the upper conductor of trunk line Z. In the private branch exchange the trunk line Z normally extends to the upper and lower windings of line relay 277 of connector H, way of the release out key, contacts of the call out key, conductors 250 and 25S, armatures 292 and 293 and their resting contacts, and the normally closed contacts controlled by armatures 295- and 296. Line relay 277 accordingly energizes. Electropolarized relay 33 included in the circuit of line relay 277 in the relay group HG does not energize at this time, however, owing to the fact that the current flowing through its upper winding opposes that flowing in its lower winding. Returning now to line relay 277, the said relay, upon energizing, closes. at armature 296, the following circuit for release relay 278: from ground by way of a pair of normally closed contacts on the blocking key, a pair of normally closed contacts on release in key, conductor 25 1-, armature 298 and its working contact, and release relay 278 to battery. Release relay 278, upon energizing, places ground on release trunk conductor 252, the said ground potential extending back to private normal conductor 21.1 by way of the resting contact of the upper spring of the r lease in key, and the said spring. By means of this ground potential on test contact 201 and its multiples in the banks of the switches, in the private branch exchange, having access to the trunk line Z the said trunk line is made busy. A branch of this circuit extends to battery through the busy visual signal 203 which energizes, thereby informing the attendant operator that the trunk line Z is in use.

In order to inform the calling operator that she has obtained connection with a t unk line such as the trunk line Z, there is a tone machine, indicated by the reference characters TM, shown in the lower part of Fig. 3. A lead from this machine is connected to bank contact 139 and also to the corresponding contact in each of the sets of contacts in which a trupk line such as the trunk inc Z terminates. This tone machine produces a series of h h frequency alternations which flow from ground, by wayof the exchange battery, upper winding of the transformer associated with tone machine TM, the associated condenser, bank contact 139, wiper 131, conductor-72, condenser 82, resting contact of armature 58 and said armature, and thence to ground by way of the lower conductor of trunk line Z. A branch of this circuit extends, by way of the right hand windings of the repeating coil T in series, to battery, by way of the upper conductor of the trunk line Z. Hence the operator hears, at this time, a distinctive tone to positively inform her that she has obtained connection with the trunk line Z or a similar trunk line. v

The toll operator, upon hearing the tone, is informed thereby that she has obtained connection with a trunk line that is designed to carry regular traflic and has no special provisions for taking care of toll calls. The calling operator may, if she deems it advis able. release the established connection and call again in an attempt to get in on the trunk line X after it has become idle. Assuming that she decides to complete the connection by way of the trunk line Z, she has two courses to-follow. She may dialthe last two digits herself or she may dial 0 thereby signalling the attendant operator and request the latter to complete the connection We shall assume first, that she decides to follow the former course.

After the toll operator is ready she may operate her calling device in accordance with'the first local digitof the desired number whereupon the line'relay 100 of selector E deenergizes a corresponding number of times and at armature 106 opensv the circuit of line relay 277 upon each 'deenergization. Each time line, relay 277 deenergizes in response to these interruptions produced in its circuit, itcloses at armature 298 thefollowing circuit for V the vertical magnet 299: from ground by way of the previously traced circuit to armature 2 98, and thence by way of its resting contact, armature 351 and its working contact, off normal springs 291 and 289, slow acting series relay 279, and vertical magnet 299 to battery. By the operation of the vertical magnet theshaftand wipers are raised step by step until the latter stand opposite the desired level of bank contacts.v Slow acting relay 279 energizes in series with the vertical magnet and serves to maintain the circuit of the said magnet intact after the off normal springs have shifted, as they do, upon the first vertical step. At the end of the vertical movement, relay 279 deenergizes and shifts the operating circuit from the vertical to the rotary magnet. V

The operator may now operate her calling device in accordance with the next digit of the desired number, whereupon the rotary magnet 286 is operated a corresponding number of times to step the wipers around to the desired set of contacts. The slow acting relay 282 is energized in multipie with the rotary magnet and serves to hold the circuit to the rotary magnet closed in case the busy relay 281 energizes while passing over busy test contacts. In case the called line is busy, the operation of connector H is identical with that already described for connector H. accordingly the busy test relay 281 energizes and at armature 360 connects a lead from a busy signalling machine to the lower heavy talkingconductor to inform the calling operator that the called line is busy.

In the present case, however, we shall assume that the line of substation A is idle when called. That being the case, slow act ing relay 282, upon deenergizing, closes at armature 361, the following circuit:- from ground by way of the working contact of a mature 350 and the saie ar'mature, armature 358 and its resting c'ontact, upper winding of switching relay 233, resting contact of armature 361 and'said arn'iature, normally closed contacts controlled by armature 36%, test wiper 369, test contact 372, private normal conductor 375, switching relay 380 of the line switch C,- and stepping magnet 332 to battery. he two switching relays and 380 energize in .series with each other and the latter clears the line switch. C of its normal battery and ground connections in the usual manner; In the connector-1E1, relay 283, upon energizing, closes a locking circuit for itself at arma ture 366,- grounds the test wiper 369 at armature 36 so as to make the called line busy to the other connectors; and at armatures 3 '3 and 367 completes the connection to the linewipers 368 and 370. Ringing current is now intermittently sent out in the usual mannerto ring the bell at the called substation.

When the called subscriberanswers, the ringcut oil relay 230 operates and at arma ture 355 closes the usual locking circuit for itself and at armatures and 357 connects the back bridge relay 276 in bridge of the called line. Back bridge relay 276, upon energizing over the called line, reverses the conductors 250 and 258 oi the trunk line 51'; as regards their connection to the windings of line relay' 277. Thisobviously reverses the direction of the current flow in the upper winding "of the electro polarized relay 33 of relay group RG. The two windingsof the said relay which heretofore have opposed each other now assist each other in operating the said relay. Upon energizing, relay closses a circuit for-reversing relay 34 at armature 55, and the said relay energizes and locks itself to grounded conductor 74 at armature disconnects to distinctive tone from therepeating coil T at armature 5S, and, at armaturesb'? and 59, reverses the conductors78 and 7 9 as regards their con nection with the windings of line relay 100 of selector his a further result of the energization of relay 33 it closes, at arm-a tare 54, a local circuit for the upper winding of battery feed relay 35 in series with resistance 81. Relay 35, upon energizing, closes the previously described local circuit for line relay 100 of selector E, at thev same time disconnecting conductors 78 and 79 entirely from the windings of line relay 100,- whereupon the current flow in the said con ducto'rs ceases and, accordingly th e'opertbtors supervisory lamp L is not lighted at this time. I

The toll operator may now converse with the subscriber at substation A in the usual manner, and, assuming that the desired subscriber and not some other has answered, she takes the necessary steps to connect the subscriber at substation A with the subscriber who desires connection with him and when such connection is completed the two subscribers may converse with each other.

When the conversation is finished the subscriber at substation A replaces his receiver, thereby opening the circuit of back bridge relay 276 of connector H. Upon deenergizing, bacl; bridge relay 276 lights the supervisory lamp at armature 294. This, however, has no particular function at this time unless the toll operator fails to release the connection. Back bridge relay 2'76 also reverses the conductors of trunk line Z back to normal, thereby reversing the current flow in them. In the relay group HG, the electropolarized relay 33 respo-ndsto this reversal of current by retracting its armatures thereby opening the circuit of relay 35 at armature 5a. Upon deenergizing, relay 35 extends the conductors 73 and 7:). to the upper and lower windings of line relay. 100 and at the same time opens the local energizing circuit of the said line relay. W hen this is done current commences to flow again in the conductors 78 and 79 and the operator is given the usual disconnect signal. 7

Upon perceiving the disconnect signal, the operator pulls down the connection.

When the plug is removed from the jack J, the selectors D and Eare released in the usual manner and the circuit of line relay 277 or" connector H is opened. energizing, line relay 2'77 opens the circuit of release relay 273. Release relay 278 upon deenergizing closes at armature 352 a circuit for the release magnet Release magnet 235 upon energizing restores the switch shaft and wipersto normal position, its circuit being broken by the oil normal con tacts 288 when the shaft reaches normal poition. All the apparatus used in making the call is now restored to normal.

We shall now consider an alternate method that may be used by the toll operator when she obtains connection with the trunk Upon deline Z, or a similar trunk line. Upon hearing the before mentioned tone and being informed thereby as to the nature of the seized trunk, and in case she knows the name of the desired subscriber but does not know his number, the operator may dial the digit 0.' Assuming that she does as above noted, the vertical magnet 299 receives ten impulses over the previously traced circuit and accordingly steps the switch shaft and wipers up to the tenth level. Upon reaching the tenth level, the switch shaft operates the spring 287 so as to force it into contact with its working contact. Upon operating, spring 287 closes the following circuit for the answering lamp: from ground by way of armature and its working contact, armature 297 and its resting contact, contact of spring 287 and said spring, conductor 256, and the answering lamp to battery, and the said lamp becomes lighted.

Upon noting the lighted condition of the answering lamp, the attendant operator throws her listening key thereby connecting the two conductors 214; and 215 or the operators head set in multiple with the conductors of trunk line Z, and placing a multiple ground on the release trunk con ductor 252 at the lower pair of contacts of the said key, by way of the lower lair cl contacts of the release in key, and the lower pair of contacts or the blocking key. As a further result of the operation of the lietening key, a circuit is closed for the calling device switching relay 220. Upon ei'iergizing, relay 220 closes the following circuit: from ground by way'ott arniature 221 and its working contact, calling device S, conductor 210, iinpulsing relay 205, normally closed contacts controlled by armature 208, a pair of springs on the listening key, conductor 251, armature 361 and its contact, and over previously traced circuit to battery, by way of the rotary magnet 286. Relay 205 energizes over the above traced circuit but neither slow acting relay 282 nor the rotary magnet 286 is able to energize on account of the high resistance of the said relay 205. Upon energizing, re lay 205 closes at armature 207 a circuit for slow acting relay 206. Upon energizing, relay 206 completes a local circuit for-impulsing relay 205 at armature 208, and at armature 213 prepares the impulsing circuit for the operatingmagnets of the connector H. As a still further result of the operation of the listening key, ground'trom the private normal conductor 211 is placed on conductor 255 at the top pair of contacts of the said key, thereby closing a circuit which extends by way of conductor 255, impedance 284-, normally closed contacts controlled by armature 354, and the upper winding of back bridge relay 276 to battery. Upon energizing, relay 276 extinguishes the answering lamp and closes a locking circuit for itself at armature 297 and at armatures 295 and 296 reverses the conductors and 258 as regards their. connection with the windings of line relay 277. In response to this reversal, the electropolarized relay of relay group RG energizes with the here inbeiore described results.

The toll operator and the attendant may now converse with each other and after obt-aining the desired information from the toll ooerator, the attendant operator throws her release in key, thereby separating the release trunk conductor 252 fromthe private normal conductor 211 and placing direct ground on the latter. As a further result of the operation or" the release in key, its lower pair of contacts opens a multiple point whereby ground is held on the release trunk conductor 252, and, at another pair of contacts, removes ground from the conductor 254- and consequently armature 298 of line relay 277. Release relay 278 now deenergizes and at armature 350 removes ground from the release trunk conductor 252 so as to unlock any relays in the switch which might be locked at this time, and at armature 352 closes the circuit of the release mag net 285, and the shaft and wipers of connector. H are accordingly restored to normal position. 1

The operator may now return her release in key to normal position, reuniting the private normal conductor 211 and the release trunk conductor 252, and immediately placing ground on the latter and also on conductor 254, thereby closing a circuit for re lease relay 278. It will be noted now that before release relay 278 energizes that there is a circuit closed from grounded release trunk conductor 252by way of armature 350 and its resting contact to battery, through cut-ofl relay 275. This relay, however, having a stiffer adjustment does not energize as quickly as the release relay 278,'and consequcntly the latter relayis able to energize and open the circuit ofthe cut off relay at armature 350, before the latter energizes, and at thesame time places a multiple ground on the release trunk conductor 252.,

The circuits are now in readiness for the mechanical operation of connector H and the operator accordingly manipulates her calling device S in accordance with the first local digitof the desired number, whereupon the impulsing relay 205 is deenergized a corresponding number of times and upon each deenergization completes the following circuit for the vertical magnet 299: from ground by way of armature 207 and its restingcontact, armature 218 and its working contact, a pair of springs on the listening or call in key, conductor 251, armature 351 and its working contact, oil normal springs 291 and 289, series relay 279, and vertical magnet 299, to battery. By the operation of the vertical magnet, the switch shaft and wipers are raised step by step in the usual manner until the latter stand opposite the desired level of contacts. In response to the next and last digit of the desired number, the rotary magnet 286 is energized a number of times to step the wipers around to the desired set of contacts, being in this case contacts 371 to inclusive.

When the called subscriber answers, the ring out otlrelay 280, upon ei'iergizing, rcmoves the intermittent ringing current from the line and connects up the back bridge relay 276 in the usual manner and at the same time opens the previously described locking circuit for the said back bridge relay. The attendant operator and the called subscriber now converse with each other and, after learning that the subscriber who answers the telephone is the one wanted and apprising the toll operator of the fact, the attendant operator restores her listening key, whereupon relays 205 and 206 deenergize. From this point the operation. continues as before and consequently does not need to be ex lained again.

We shall now consider still another varia tion of an incoming call from the toll operator that might well arise. It sometimes happens that the attendant operator considers it advisable to block all incoming calls, i. e., she throws her blocking key and with the key in this position her answering lamp is lighted as soon as the trunk line Z is seized in the main exchange and the calling operator is unable to operate the connector H owing to the fact that direct ground is removed from the armature of line relay 277 by the operation of the blocking key. A current sufficiently strong to operate the release relay 278, but too weak to operate the vertical magnet 299, is allowed to pass through the resistance 212. Assuming that the blocking key is thrown when a toll call, such as the one previously described, comes in over the trunk line Z, release relay 278, upon energizing, closes at armature 352 the following circuit for the answering lamp: from ground by way of armature 352 and its working contact, armature 297 and its resting contact, armature 356 and its resting contact, conductor 257, the upper pair of confacts of the blocking key, and the answering lamp to battery. The operator, upon not ing the lighted condition of the answering lamp, throws her listening key and the call proceeds thereafter in the same manner as previously described except that it is not necessary for her in this case to release the switch as it has not yet been operated.

ttention will now be called again to the trunk line X and its associated equipment in the branch exchange. It sometimes happens that the attendantoperator is forced to be absent, at night for instance, or at other times when there are other persons at the establishment served by the private branch exchange. In this event, one substation, the substation A for example, is setaside for the reception of all toll calls. Theattendant operator, before leaving, calls the substation A by way of the connector ll ard waits until the subscriber thereat answers. After learning the nature of the call, the subscriber at substation A replaces his receiver. The attendant operator then restores her keys to normal position but does not operate the release key, and accordingly the connection is not released. The trunk line X now extends from the bank contacts 134; and 137 of, the selector E in the main exchange straight through to the bridged bell at the substation A, and when a call comes in the said bell is rung in the usual manner, and all the toll calls for the private branch exchange are received thus until the attendant operator returns again.

F or the sake of completeness we shall now consider briefly the operation of the equipment in completing regular calls to and from the private branch exchange as well as calls between the various subscribers of the said exchange. Considering first the calls coming in from the main exchange, the bank contacts 151L152, inclusive, associated with the repeater F, Fig. 3, are assumed to be in the banks of a second selector switch in the main exchange. Now when the main exchange subscriber dials two suitable digits, the said second selector is caused to rotate in search of an idle trunk line, such as the trunk line Z. Assuming that the said trunk line is the first one found idle, the before mentioned selector upon switching through, places a ground potential on test contact 151 immediately and the said ground potential extends by way of private'normal conductor 192 to test contact 140 and its multiples in the banks of the toll switches having access to the trunk line Z, thereby making the said trunk line busy. The operation of the switching relay 176 of line switch C is the same in this case as though the trunk line Z were seized by the selector E. Considering briefly the operation of repeater F, it may be stated that the line relay 155, upon energizing, closes a circuit for release relay 158 which places ground on the private normal conductor 19-2, at armature 170, before it is removed by the selector which seized the trunk,thereby establishing the usual holding circuit for the said selector. As a further result of the energization of line relay it places a bridge across the conductors of same when it is seized by a regular selector as when seized by the toll selector E. Now when the calling subscriber operates his calling device for the neXt digit the interruptions produced in the circuit of line relay 155 are reproduced in the circuit of line relay 277 of connector H at armature 163. It is thought that with these few remarks the operationof thetrunk line Z-in connection with an incoming regular call will be suiticie'ntly well understood. 3

lVe shall now assume that the subscriber at substation A desires to make a call. lVhen the receiver is removed at substation A a circuit is closed over line conductors 374 and 376 tor the line relay 381 of the line switch C. Uaon ener izin rela 1 381 closes at armature 387 a circuit for the switching relay 380 and the stepping magnet .382 in series, and at armature 386 connects the test wiper 389 to a point between the said switching relay and the said stepping magnet. The operation now depends upon whether the test contact, upon which thetest wiper 389 is standing, is busy or idle. If it is busy there is a ground potential on it, the switching relay 380 is short circuited, and the stepping magnet 382, which interrupts its own circuit, is operated in the manner of a buzzer to advance the wipers 388390, i elusive in search of an idle trunk-line. In the present case, however, we shall assume that the trunk line terminating in bank contacts 391 393, inclusive, is idle. That being the case, switching relay 380 is not short circuited and accordingly energizes. Stepping magnet 382, however, is not energized at this time because of the high resistance of the switching relay. Upon energizing, relay 380 grounds the test wiper 389 at armature 38 i and at armature 383 and 385 extends the connection to the trunk line terminating in bank contacts 391, 392 and 393. As has been mentioned before this trunk line is assumed to extend to and terminate in the line relay of a selector connector. Accordingly, the'line and rel-ease relays of the said selector contact, and cut off relay 275 to battery. Relay nector immediately energize and the latter places ground on the release trunk conductor of the seized trunk line before the line relay 381 of line switch C has had time to deenergize. By means of this ground potential on testcontact 392 and its multiples in the banks of the line switches, the seized trunk is made busy to the'line switches having access to. it. This ground potential also extends back by way of armature 384C and its working contact to the switching relay380 to hold the said relay in its operated position. A branch of this holding circuit extends by way of private normal conductor 375 to multiple test contacts, such as test contacts 372 and 378, in the banks of the connectors there'- by guarding the line of substation A against intrusion in the usual; manner.

The calling subscriber may now operate his calling devlce 1n accordance with the first digit of the desired number whereupon the selector connector, to which the connection has been extended raises its shaft and wipers step by step until the latter stand opposite the desired'levelof bank contacts. i I

The operation now depends upon whether the digit called is 0, which is the digit called when a main exchange numberis desired, or some other digit Assuming first that the digit called is some digit other than 0, the circuits, at the end of the vertical movement, are put into condition for the calling of neXt digit whichwill cause the switch to operate as a connector to' give access to a line in the private branch eX change in the usual manner. V I

Assuming now that the calling subscriber operated his calling device S in accordance with the digit 0, the selector connector to which the connection has been extended steps its wipers up to the tenth leveland rotates them in search of an idle trunk line leading to the main exchange. lVe shall assume in the present case that the trunk line Z which terminates in the bank .contacts 200 to 202., inclusive, Fig. 5, assumed to be in the bank of the selector connector, is the first one found idle and consequently theone selected. The selector connector ac cordingly switches through thereby extendingfia talking connection from the line of substation A to the, line contacts 200 and 202 trunk line Z, and places a ground potential upon test contact 20l'so as to make the seized trunk line busy to theo'ther switches in the privatebranch exchange having accessto it. This ground potential extends by way of private normal conductor 211-to the visual signal 203 and the said signal accordingly becomes operated. A branch ofthe energizing circuit for the visual signal 203 extends by way of the upper spring of the release in key and its resting contact release trunk con ductor 252, armature 350 and its resting con- 275, upon energizing, removes the bridge o t the windings of line relay 277 of connector H from the conductors of trunk line Z and connects the said connectors to bank contacts 200 and 202, thereby, finally extendingthe line of substation A to the conductors of trunk line Z.

When the lineof substation A is thus1eX' ten'ded the line relay 172 of the line switch 0 in'the main exchanga'is energized and at armature 182 closesw a circuitf forf the switching .relay 176 and the stepping magnet 17 5 in series, at the same t-ime'placing ground on the private normal conductor 192 thereby making the trunk line busy to the switches having access to" it in the main exchange. The line switch Cis new oper ated in the same manner as described for line switch C and accordingly rotates its wipers in search of an idle trunk line. The trunklines terminating in the bank contacts of line switch C are assumed to be connected at the other end to first selector switches. That being the case, the line switch C, upon operating, gives access to a first selector switch, and the line and release relays of the said selector immediately energize and prepare the switch for operation in the usual manner, at the same time placing ground on the release trunk conductor to establish the, usual holding circuits for the line switch C and to maintain the trunk line Z busy. Fromthis point the operation is old and need not be considered.

Having described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

v VVhat I claim as my'invention is:

1. In a telephone system, main and branch exchanges, a group of trunk lines connecting said exchanges for use in handling regular interexchange connections, a toll trunk line connecting said exchanges for use only .in connecting toll lines with lines in the branch exchange, and tell selectors in the main exchange responsive to a particular digit for connecting with said toll trunk, and responsive to the same digit for connecting with an idle trunk in said groupin case the said toll trunk is busy.

2. In a telephone system, main and branch exchanges, a group of trunk lines connecting said exchanges for use in han dling regular interexchange connections, a toll. trunk line connecting said exchanges for use only in connecting toll lines with lines in the branch exchange, and toll selectors in the main exchange having bank contact sets arranged in groups, the said toll trunk being terminated in the first set of bank contacts in a certain group, while the said first mentioned trunklines are terminated in the other sets of contacts in the samegroup. V I 7 3. In a telephone system, a selector switch controllable by an operator,- two groups of trunk lines accessible to, said selector, the trunk lines of the first group having preference over the trunk lines of the other groupindependent of control by the operator, and means for giving the operator a distinctive signal whenever a trunk line of the second group is selected, said means comprising a special test wiper in said switch and a signalling circuit completed over said wiper.

4E. In'a telephone system, main and branch exchanges, a toll trunk line connecting said exchanges, a toll selector in the main exchange controllable by a toll operator for connecting with said trunk line, a plurality of other trunk lines connecting the main and branch exchanges which are accessible to said toll selector only when the said toll trunk is busy, subscribers? selectorshaving access to said other trunk lines but not to said toll trunk, and means for giving the toll,

operator a signal to notify her when one of said other trunk lines is selected in place'ot the toll trunk, said signalling means being inoperative in case one of said other trunk lines is seized by a subscribers selector.

5. In a telephone system, main and branch exchanges, a toll trunk line connecting said exchanges, a toll selector in the main ex change controllable by a toll operator for connecting with said trunk line, a plurality of other trunk lines connecting the main and branch exchanges which are accessible to said toll selector only when the said toll said toll selector only when the said toll trunk busy, means for transmitting a distinctive aud ble tone to the toll operator whenever one of said other trunk lines is 7 connected with in place of the said toll trunk, means for extending the connection to a called line, and means for disconnecting the tone during conversation. V I i 7. In a telephone system, main and branch exchanges, a toll trunk line connecting said exchanges, a toll selector in the main exchangecontrollable by a toll operator for connecting withsaid trunk line, a plurality of other trunk lines connecting the'inain and branch exchanges which are accessible to said toll selector only when the said toll trunk 18 busy, incoming connector'switches vin which the said vtrunk lines terminate at the branch exchange, an operators position at the branchexchange, and circuit arrange ments such that the branch operator is re-- quired to operatethe associated incoming.

connector in case the said toll trunk is taken for use by the toll operator, while if one of said other trunk lines is connected with the" toll operator can operate the associated incoming connector herself.

8. In a telephone system, main and branch exchanges, a toll trunk line connecting said exchanges, a toll selector in the main GX'T' change controllable by a toll operator "for connecting with said trunk'line, a plurality I, a V V or other-trunk linesconnecting the main and branch exchanges which are accessible to said toll selector only when the said tollj lit? 7 trunk is busy, an operators POSlt at the branch exchange, and circuit arrangements,

such that the toll operator can signal the branch operator direct overthe said toll trunk by ringing thereove'r, whereas in case one of said other trunk lines is taken for use the toll operator is required to call an other digit to signal the branch operator.

In a telephone system, main and branch exchanges, a toll trunk line coi'ine'cting said exchanges, a toll selector in the main excl ange Controllable by atoll operator for connecting with said trunk line, a plurality of other trunk lines connecting the main and branch exchanges which are accessible to said toll selector only when the saidtoll trunk is busy, a supervisory signal at the toll operators position, and means for actuating said signal during the establishment oi connection to the branch exchange only in case the connection is established by way or said toll trunk. 10. In a telephone system, main and branch exchanges, a toll trunk line connectin" said exchanges, a toll selector in the main exchange controllable by a tol operator for connecting with said trunk line, a plurality of other trunk lines connecting the main and branch exchanges which are accessible to said toll selector only when the said toll trunk is busy, a supervisory lamp at the.

toll operators position, means for lighting said lamp during the establishment of a connection to a branch exchange subscriber and also when such subscriber hangs up, pro vided the connection is-established'by way of said toll trunk, and circuit arrangements such that if the connection is established by way of one of said other trunks the said lai p is lighted only when the called subs her hangs up.

11. In a telephone system, meansincluch m an operatorls cord circuit and a series automatic switches for extending a connection to a called subscribersline, a supervisory lamp at said cord circuit, means for prerenting the lighting of said lamp by holding its circuit open during the establish-. ment its circuit when the called subscriber hangs up to iect signal.

12. In a telephone system, means includ- :ing an operators cordcircuit and a trunk line or extending a. connection to a called subscrib: s line, a polarized relay in said cord circuit controlling a supervisory lamp, said relay being irresponsive to normal current iiow over said trunk line, means for reversing the direction of current flow in said trunlr line when the called subscriber answers, means for interrupting the flow'of current in said trunk line at the same time so as to prevent the operation of said relay,

'ma'gn'ets, a line or the connection and during convers'a-c and means for lighting said lamp'by give the operator 'adis and means for reestablishing the flow of current over said trunk line in the reverse direction when the called subscriber hangs up, whereupon said relay is operated to light said lamp.

13. In a telephone system, an automatic switch, operating magnets for said switch, relays in said switch for controlling said circuit over which said switch is operable from one point through the medium of said relays, and a second circuit over which current impulses may be transmitted direct to said magnets from another point to operate said switch inclependent oi said relays.

let. In a telephone system, two exchanges, an automatic progressively movable switch in one exchange, operating magnets for said switch, an operators position in each exchange from which said switch may be con trolled, a circuit arrangement including relays in said switch whereby the operator in one exchange can control said magnets, and a circuitarrangement for controlling said magnets direct from the oper-ators position in the other exchange without any intervening relays.

. 15. In telephone system, a group of automatic switches, operating magnets in each switch, a fast and slow relay combinatie-n in each switch for controlling the as sociated operating ma nets, and a fast and slow relay combination common to all of said switches and adapted to be used to control the operating magnets of any one of said switches in place of the relay combination normally assigned thereto.

16. Ina telephone system, a group of automatic switches, operating magnets in each switch; a fast and slow relay combination in each switch for controlling the associated operating magnets, a fast and slow relay'combinaticn common to all of said switches and adapted to be used to control the operatingmagnets of any one of rid switches in place of the relay combination normally assigned thereto, and a plurality of keys for actuation by an oper to associate the said common relay combination with desired ones of said switches will. I

1-7. In an automatic telephonosystcm, an automatic switclnan operating magnet for said switch, a line relay and a release relay jointly controlling said operating m. both of said relays being quick acting, release magnet controlled by said release relay, a circuit for said release relay controlled by said line relay, and another circuit for maintaining said release relay energized during momentary deenergizations of said line relay while the switch is bein operated, said other circuit including manually operable contacts at an operator-ls position.

18. In a telephone system, an automatic 

